1. Field of the Invention
The present invention relates to an automatic continuous variable transmission. More particularly, the invention relates to a centrifugal roller weight used in an automatic continuous variable transmission or the like found in motor vehicles, boats or watercrafts, or auxiliary mechanisms. Each centrifugal roller weight comprising a core weight and an outer cover made of wear-resistant resin is provided between a ramp plate and a movable drive pulley half of a drive pulley in the automatic transmission mentioned above. Upon a centrifugal force, the centrifugal roller weights move radially in the drive pulley to continuously change the width of the grooves of the drive pulley and a driven pulley while the drive pulley and driven pulley are mounted around by an endless belt, so as to change the vehicle speed continuously.
2. Description of the Prior Art
A conventional automatic continuous variable transmission (i.e., CVT) 1 of a motor vehicle is illustrated in FIG. 1 and it comprises a drive pulley 2 proximate to an engine 12, a driven pulley 3 at a rear axle, and an endless trapezoid-section belt 9 (i.e., V-belt 9) rotatably interconnected with the drive pulley 2 and the driven pulley 3. In the operation, a piston 8 is activated when the engine 12 starts. Next, a rotary shaft 10 rotates to revolve the drive pulley 2. A plurality of centrifugal weight rollers 6 (i.e., weight roller 6) in a movable drive pulley half 4 move radially outward upon a centrifugal force acting thereon. A ramp plate 7 is fixed; hence, the movable drive pulley half 4 moves toward a stationary drive pulley half 5 due to an opposite reaction, and forces exerted on sides of the V-belt 9 push the V-belt 9 of the drive pulley 2 to move outward. Thus, the effective diameter of the V-belt 9 of the drive pulley 2 increases and, at the same time, the V-belt 9 of the driven pulley 3 moves toward the rotary shaft 10 and the effective diameter of the V-belt 9 of the driven pulley 3 decreases. As the revolution of engine changes, the centrifugal force acting on the weight roller 6 is changed. Thus, the distance between the movable drive pulley half 4 and the stationary drive pulley half 5 is changed. As a result, the continuous change of effective diameters of V-belts 9 of the drive pulley 2 and the driven pulley 3 changes the speed of vehicle. Such a conventional continuous variable transmission 1 of motor vehicle is disclosed in U.S. Pat. No. 4,925,432. The shape of the weight roller 6 in the movable drive pulley half 4 is spherical (see U.S. Pat. No. 2,986,043) or cylindrical (see U.S. Pat. No. 4,925,432).
The weight roller 6 is at a lowest position in the movable drive pulley half 4 when the revolution of engine is lower than a predetermined value or centrifugal force acting on the weight roller 6 is very small (see FIG. 2). At this position, the effective diameter (2hR0) of the V-belt 9 in the drive pulley 2 is a minimum and the effective diameter of the V-belt 9 in the driven pulley 3 is a maximum. The transmission 1 is in a low gear status when the weight roller 6 is at its lowest position (see FIG. 2).
The revolution of the drive pulley 2 is higher than that of the driven pulley 3 when the motor vehicle starts. For example, the drive pulley 2 may rotate three times while the driven pulley 3 rotates once. This means a reduction gear ratio 3:1 in low gear status, when the vehicle speed is slow but the engine has a large torque.
As the revolution of engine increases, the centrifugal force acting on the weight roller 6 increases correspondingly. While weight rollers 6 gradually move radially outward, the effective diameter of the V-belt 9 in the drive pulley 2 increases and the effective diameter of the V-belt 9 in the driven pulley 3 decreases correspondingly. This continuous changing of the effective diameter of the V-belt of the drive pulley 2 and that of the driven pulley 3 shows the continuous gearshifting of the automatic transmission.
The weight roller 6 is at a highest position in the movable drive pulley half 4 (see FIG. 3). At this position, the effective diameter (2hR) of the V-belt 9 of the drive pulley 2 is a maximum and the effective diameter of the V-belt 9 of the driven pulley 3 is a minimum. The transmission 1 is in a high gear status when the weight roller 6 is at its highest position (see FIG. 3). At this position, the revolution of the drive pulley 2 is lower than that of the driven pulley 3. For example, the drive pulley 2 may rotate 0.9 times while the driven pulley 3 rotates once. This means a reduction gear ratio 0.9:1 in high gear status, when the vehicle speed is fast but the engine has a small torque.
From the mechanism of prior art, we can understand that if the sizes and angles of the drive pulley 2, the driven pulley 3, and other related parts are fixed, and sizes of weight rollers 6 are fixed, then the lowest position (see FIG. 2) and highest position (see FIG. 3) of the weight roller 6 in the movable drive pulley half 4 are fixed. Thus, reduction gear ratios of low gear status and high gear status in the transmission are unchangeably fixed. However, when the weight rollers 6 wear after a period of time of use, reduction gear ratios of low gear status and high gear status then deteriorate undesirably. This in turn adversely affects a gearshifting performance of the motor vehicle.
In the prior art it is typically to decrease weight of the weight roller 6 for increasing driving power. In this arrangement, the required revolution of the engine for a clutch 11 to engage and for the vehicle to start will increase to a value larger than the predetermined required value. Thus, the vehicle can start powerfully. However, the centrifugal force in this arrangement is therefore not large enough, and the effective diameter (2hR) of the V-belt 9 of the drive pulley 2 is decreased, so the maximum vehicle speed is decreased, due to lighter weight rollers 6. On the contrary, increasing weight of the weight rollers 6 will increase the centrifugal force and decrease the required revolution of the engine for the clutch 11 to engage and start the vehicle. Thus, the vehicle starts relatively weakly. However, because of heavier weight rollers 6, the centrifugal force is larger and the effective diameter (2hR) of the V-belt 9 of the drive pulley 2 is increased, and therefore the maximum vehicle speed is increased.
In the prior art it is also found that, when the weight rollers 6 are at its highest position (see FIG. 3), surfaces of the weight rollers 6 contacted with the ramp plate 7 may easily be worn or scraped due to low precision of the ramp plate 7. As those stated above, when the weight rollers 6 are worn and their sizes become smaller, the distance that the movable drive pulley half 4 can move is shorter and the effective diameter (2hR) of the V-belt 9 of the drive pulley 2 is decreased. As a result, reduction gear ratios of low gear status and high gear status of the transmission will then deteriorate significantly.
From those stated above we understand that, in the said centrifugal automatic transmission, using weight rollers 6 in the movable drive pulley half 4 of the drive pulley 2 has the following disadvantages: (1) Surface of the weight roller 6 usually wear abnormally when the weight roller 6 is at its highest position (see FIG. 3). Thus, reduction gear ratios of low gear status and high gear status can deteriorate significantly. (2) Changing weight of the weight roller 6 merely cannot increase both the initial acceleration and maximum vehicle speed of the motor vehicle simultaneously. (3) If sizes and angles of the drive pulley 2 and the driven pulley 3 are retained unchanged, it is not possible to use means of weight rollers 6 to adjust reduction gear ratio of low gear status or high gear status, and it is not easy to adjust driving performance either. Thus, the need for improvement exists.